Apparatus and methods for adjusting voltage controlled oscillator gain

ABSTRACT

Apparatus and methods for adjusting a gain of an electronic oscillator, such as a voltage-controlled oscillator (VCO), are disclosed. In one aspect, an apparatus for compensating for VCO gain variations includes a charge pump controller. The charge pump controller can be configured to select a VCO gain model based on a comparison of a VCO gain indicator and a threshold value stored in a memory, obtain VCO gain model parameters from the memory corresponding to the selected VCO gain model, and compute a charge pump current control value using the VCO gain model parameters. The charge pump current control value can be used to compensate for VCO gain variations.

BACKGROUND

1. Field

The disclosed technology relates to electronic systems and, inparticular, to voltage-controlled oscillators.

2. Description of the Related Art

Electronic parts, such as wide-band synthesizers, can support a widerange of output frequencies. To create a range of output frequencies, anelectronic oscillator configured to oscillate within a range offrequencies, such as a voltage-controlled oscillator (VCO) can be used.In some applications, a wide range of output frequencies may be desired.For example, an output signal ranging from about 400 MHz to 6.3 GHz maybe desired. To ensure high-performance within the entire frequencyrange, more than one VCO may be implemented. In such an implementation,each VCO may be dedicated to a specific frequency band, which mayoverlap with a frequency band of another VCO. Tuning the frequency of aVCO may impact the gain of the corresponding VCO. As frequency of a VCOis tuned and the corresponding gain is modified, this can lead tosuboptimal performance. For systems that include a plurality of VCOs,compensating for changes in VCO gain can be more complicated.Accordingly, a need exists for improved systems and methods forcompensate for VCO gain variation.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

The methods and apparatus described in the claims each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, some prominentfeatures will now be briefly discussed.

One aspect of this disclosure is a method of adjusting avoltage-controlled oscillator (VCO) gain. The method includes selectinga VCO gain adjustment model based on a VCO gain indicator. The methodalso includes obtaining VCO gain adjustment model parameters from amemory. Using the VCO gain adjustment model parameters, a charge pumpcontrol value is computed. The overall loop gain of the phase-lockedloop is dynamically adjusted using the charge pump control value.

According to some implementations, the VCO gain indicator is indicativeof a VCO output frequency. In various implementations, the VCO gainindicator is indicative of a capacitance value in a tunable capacitancecircuit configured to control a frequency of a VCO output. In some ofthese implementations, selecting the gain adjustment model includescomparing the capacitance value to a threshold value.

In accordance with a number of implementations, the gain adjustmentparameters include a slope and an offset. In some implementations,obtaining VCO gain adjustment model parameters is based on a VCOselected from a plurality of VCOs.

In certain implementations, the method further includes computing theVCO gain model parameters, and storing the VCO gain model parameters tothe memory.

Another aspect of this disclosure is an apparatus that includes a chargepump controller. The charge pump controller is configured to: select aVCO gain model based on a comparison of a VCO gain indicator and atleast one threshold value stored in a memory; obtain VCO gain modelparameters, from the memory, corresponding to the selected VCO gainmodel; and compute a charge pump control value using the VCO gain modelparameters.

In some implementations, the VCO gain indicator is indicative of VCOoutput frequency. According to a number of implementations, the VCO gainindicator is indicative of a capacitance value in a circuit configuredto control a VCO output frequency, and the threshold values stored inthe memory represent threshold capacitance values. According to variousimplementations, the VCO gain model parameters correspond to a pluralityof VCOs, and the charge pump controller is further configured to obtainVCO gain model parameters corresponding to one VCO selected from theplurality of VCOs. In some implementations, the VCO gain modelparameters include at least a slope and an offset.

According to a number of implementations, the charge pump controller isconfigured to dynamically cause a gain of a VCO to be adjusted based onthe charge pump current control value. In various implementations, theVCO gain model represents a portion of a VCO correction curve, the VCOcorrection curve representing the VCO output frequency indicator versusthe charge pump current control value.

In accordance with some implementations, the apparatus further includesa phase-locked loop, the phase-locked loop including a VCO and a chargepump, the charge pump configured to: receive the charge pump currentcontrol value from the processor, and adjust a gain of the VCO based onthe charge pump current control value.

According to certain implementations, the charge pump controller isfurther configured to compute the VCO gain model parameters and the atleast one threshold value, and to store the VCO gain model parametersand the at least one threshold value to the memory. In some of theseimplementations, the charge pump controller is configured to compute theVCO gain model parameters in response to detecting a calibration event.

In certain implementations, the apparatus further includes the memory tostore VCO gain model parameters and threshold values. In accordance withsome of these implementations, the memory includes at least one look-uptable to store at least one of the threshold values and the VCO gainmodel parameters.

Yet another aspect of this disclosure is an apparatus that includes:means for selecting a VCO gain model based on a comparison of a VCO gainindicator and at least one threshold value stored in a memory; means forobtaining VCO gain model parameters from the memory corresponding to theselected VCO gain model; and means for computing a charge pump currentcontrol value using the VCO gain model parameters.

In some implementations, the apparatus is a mobile device.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a mobile device, which can include aphase-locked loop.

FIG. 2 schematically illustrates a phase-locked loop, according to oneembodiment.

FIG. 3A shows an example circuit that can control voltage-controlledoscillator (VCO) frequency. FIG. 3B illustrates a relationship betweengain and capacitance in a voltage-controlled oscillator (VCO) controlledby the example tunable capacitance circuit shown in FIG. 3A. FIG. 3Cillustrates the relationship between gain and frequency in a synthesizerhaving a plurality of VCOs.

FIG. 4 is a flowchart of an illustrative method of compensating for VCOgain variation, according to one embodiment.

FIG. 5 is a block diagram of a circuit that can compensate for VCO gainvariation, according to an embodiment.

FIG. 6 schematically illustrates a circuit that can compensate for VCOgain variation, according to another embodiment.

FIG. 7 is a plot of example VCO correction curves.

FIG. 8 is a flowchart of an illustrative method of calibrating VCO gainadjustment model parameters, according to an embodiment.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Generally described, aspects of the present disclosure relate toadjusting a gain of an electronic oscillator, such as avoltage-controlled oscillator (VCO). For illustrative purposes, thedescription will be provided with reference to a VCO, although theprinciples and advantages may be applied to any electronic oscillator. AVCO may be part of a phase-locked loop (PLL), which may be included in atransmit and/or receive path of a mobile device, such as a cellularphone, or a base station. A gain of the VCO can be impacted by a numberof factors, such as VCO output frequency and/or temperature. Yet,overall gain of a closed loop within a PLL can help to achieve bestperformance and/or stabilized loop bandwidth. Thus, compensating forfactors that impact VCO gain can advantageously improve VCO performance,which in turn can also improve performance of any device that includesthe VCO.

According to the disclosure provided herein, VCO gain can be dynamicallycompensated for such that the overall loop gain of a phase-locked loopis held substantially constant. This may include, for example,controlling a charge pump current based on an indicator of VCO gain,such as an indicator of VCO output frequency. A VCO gain correctioncurve can be partitioned into a plurality of VCO gain models. Dependingon the VCO gain indicator, a particular VCO gain model can be selected.For implementations that include a plurality of individual VCOs, a VCOgain model can be chosen for the selected VCO. From the VCO gain modelparameters and the indicator of VCO gain, a charge pump current valuecan be computed. The charge pump current value can then be used toadjust overall loop gain of the phase-locked loop.

The methods, apparatus, and computer readable media for compensating forVCO gain variations described herein may be able to achieve one or moreof the following advantageous features, among others. First, an optimumcharge pump current can be provided across an entire VCO outputfrequency range. Second, a charge pump controller can program a memory(e.g., a lookup table) only once, and may not need to compute andprogram the charge pump controller after each frequency change. Third,for architectures with multiple VCOs, the charge pump controller may notbe required to read the active VCO in order to compute the charge pumpcurrent control value.

Any of the methods, apparatus, and computer readable media for adjustingVCO gain described herein can be implemented in a variety of electronicdevices, such as a base station or a mobile device. FIG. 1 schematicallydepicts a mobile device 11. Examples of the mobile device 11 include,but are not limited to, a cellular phone (e.g., a smart phone), alaptop, a tablet computer, a personal digital assistant (PDA), anelectronic book reader, and a portable digital media player. Forinstance, the mobile device 11 can be a multi-band and/or multi-modedevice such as a multi-band/multi-mode mobile phone configured tocommunicate using, for example, Global System for Mobile (GSM), codedivision multiple access (CDMA), 3G, 4G, and/or long term evolution(LTE).

The mobile device 11 can include a transceiver component 13 configuredto generate RF signals for transmission via an antenna 14, and receiveincoming RF signals from the antenna 14. The transceiver 13 can alsoinclude one or more phase-locked loops (PLLs) 17 in a receive and/or atransmission path. Each PLL 17 can each include one or more VCOsconfigured to generate output signals within a frequency band. The PLL17 can be used, for example, in up-converting a signal in a transmitpath and/or down-converting a signal in receive path. Although theexample phase-locked loop 17 is illustrated in the context of atransceiver 13, any component of a phase-locked loop described hereincan be implemented in a receiver, transmitter, and/or other electronicsystems with a need for a voltage-controlled oscillator.

One or more output signals from the transceiver 13 can be provided tothe switching component 12 using one or more transmission paths 15,which can be output paths associated with different bands and/ordifferent power outputs, such as amplifications associated withdifferent power output configurations (e.g., low power output and highpower output) and/or amplifications associated with different bands.Additionally, the transceiver 13 can receive signal from the switchingcomponent 12 using one or more receiving paths 16.

The switching component 12 can provide a number of switchingfunctionalities associated with an operation of the wireless device 11,including, for example, switching between different bands, switchingbetween different power modes, switching between transmission andreceiving modes, or some combination thereof. However, in certainimplementations, the switching component 12 can be omitted. For example,the mobile device 11 can include a separate antenna for eachtransmission and/or receiving path.

In certain embodiments, a control component 18 can be included andconfigured to provide various control functionalities associated withoperations of the switching component 12, the power amplifiers 17,and/or other operating component(s). Additionally, the mobile device 11can include a processor 20 for facilitating implementation of variousprocesses. The processor 20 can be configured to operate usinginstructions stored on a non-transitory computer-readable medium 19. Theprocessor 20 can implement any combination of features of thetransceiver 13.

FIG. 2 schematically illustrates an example phase-locked loop 100. Aphase-locked loop (PLL) can be a closed-loop, frequency-control systembased on the phase difference between an input reference signal (e.g.,an input clock) and a feedback signal (e.g. a feedback clock) of acontrolled oscillator. The PLL can generate an output signal having aphase related to the phase of the input reference signal. The PLL can beimplemented by electronic circuits. As illustrated, the phase-lockedloop 100 includes a reference divider 102, a phase frequency detector104, a charge pump 106, a loop filter 108, a VCO 110, a PLL divider 112,an output divider 114, and an output amplifier 116. A charge pumpcontroller 120 can also be included. It will be understood that fewer orgreater components may implement a PLL. For example, in some instancesthe reference divider 102, the output divider 114, and the outputamplifier 116 may not be included.

The reference divider 102 can receive an input clock and generate areference clock signal having a frequency of the input clock divided byM. The phase frequency detector 104 can receive the reference clocksignal and align an edge of the reference clock (e.g., a rising edge) tothe feedback clock generated by the PLL divider 112. The PLL divider 112can generate the feedback clock from the VCO output. The feedback clockcan have a frequency of the frequency of VCO divided by N. The phasefrequency detector 104 can detect a relative difference in phase andfrequency between the reference clock and the feedback clock.

Based on whether the feedback clock frequency is lagging or leading thereference frequency, the phase frequency detector can provide controlsignal(s) to control the charge pump 106 that indicate that the VCO 110should operate at a higher or a lower frequency. However, when thefeedback clock and the reference clocks are aligned, the VCO frequencymay remain the same. If the charge pump 106 receives an indicator thatthe frequency of VCO should be increase, current can be driven into theloop filter 108. Conversely, if the charge pump 106 receives anindicator that the frequency of VCO should be decreased, current can bedrawn from the loop filter 108. Additionally, the charge pump 106 cangenerate a VCO gain adjustment indicator, which can be used to adjust again of the VCO output to the VCO 110 via the loop filter 108. The gainof the VCO output can be adjusted while maintaining a constant VCOoutput frequency.

The loop filter 108 can generate a control voltage based on one or moresignals from the charge pump 106. The control voltage can be used tobias the VCO 110. Based on the control voltage, the VCO 110 canoscillate at a higher or lower frequency, which can affect the phase andfrequency of the feedback clock. The VCO 110 can stabilize once thereference clock and the feedback clock have substantially the same phaseand frequency. The loop filter 108 can filter out jitter by removingglitches from the charge pump 106, thereby preventing voltageover-shoot.

In some implementations, the VCO 110 can include a plurality ofindividual VCOs. For instance, in some implementations, 2 to 8 VCOs maybe included in VCO 110. In implementations with a plurality of VCOs,each of the plurality of VCOs can generate an output within a specificfrequency band that overlaps with a corresponding frequency band ofanother VCO. With a plurality of VCOs, one individual VCO of the VCO 110can be selected to generate the VCO output, based on the desired outputfrequency. In this way, a wide range of output frequencies can begenerated with high-performance within the entire range of VCO outputfrequencies.

The VCO output can be provided to the PLL divider 112 and the outputdivider 114. The output divider 114 can generate an output divider clockhaving an output divider signal that is less than the VCO outputfrequency. The output amplifier 116 can receive the output divider clockand provide an amplified output signal.

Additionally, the PLL 100 includes a charge pump controller 120. Anycombination of the features of any of the charge pump controllersdescribed herein may be implemented on a processor, for example, theprocessor 20 of FIG. 1. In some instances, a processor that includes thePLL 100 and a charge pump controller 120 can be a synthesizer, such as awide-band synthesizer. The charge pump controller 120 may be implementedon either the same integrated circuit or a separate integrated circuitfrom one or more of the other illustrated components of the PLL 100.Moreover, the charge pump controller 120 can be implemented using anysuitable combination of analog and/or digital circuitry.

The charge pump controller 120 can provide a charge pump current controlvalue to the charge pump 106, which can be used to compensate for a VCOgain variation K_(v). For example, based on the charge pump currentcontrol value, the charge pump 106 can send a VCO gain adjustmentindicator to adjust a gain of the VCO output to the VCO 110 via the loopfilter 108. The VCO gain adjustment indicator can then adjust the gainof the VCO output without changing VCO output frequency. In someinstances, the VCO gain adjustment indicator can control the charge pumpcurrent by switching in one or more capacitive circuit elements inparallel with the charge-pump output, which can affect an overall loopgain. More details regarding the charge pump controller 120 will beprovided later with reference to FIGS. 4-6.

The VCO gain K_(v) can vary based on a parameter indicative of VCOfrequency. For example, a parameter used to control VCO frequency canalso be indicative of the VCO gain K_(v). FIG. 3A provides an examplecircuit that can control VCO frequency. In particular, FIG. 3Aillustrates a tunable capacitance circuit 130 that can adjust VCO outputfrequency. In implementations in which a PLL includes a plurality ofindividual VCOs, a separate tunable capacitance circuit 130 can be usedfor each VCO. Although capacitance of a tunable capacitance circuit isdescribed as an example parameter that is indicative of VCO gain, otherparameters can alternatively or additionally be used as an indicator ofVCO gain and/or VCO output frequency.

The tunable capacitance circuit 130 can include a plurality ofcapacitors 132 a-132 h and an inductor 134 that can form an LC tank.Effective capacitance of the LC tank can be adjusted using capacitancecontrol signals that can add and/or remove additional capacitance fromthe effective capacitance, which can represent the combined capacitanceof the tunable capacitance elements that are part of the LC tankcircuit. For instance, each capacitor 132 a-132 g of the LC circuitshown in FIG. 3A can be selectively included or excluded from theeffective capacitance of the LC tank based on values of the capacitancecontrol signals CAP_CTRL[0:6] opening and/or closing switches, such astransistors. With additional capacitance, the VCO frequency candecrease. Conversely, with reduced capacitance, the VCO frequency canincrease. The resonant frequency ω of the VCO can be proportional to thereciprocal of the square root of the inductance L times the capacitanceC, for example, as represented by the following equation:

$\omega = {\frac{1}{\sqrt{L*C}}.}$

FIG. 3B illustrates a relationship between VCO gain K_(v) and effectivecapacitance in the example tunable capacitance circuit shown in FIG. 3A.As shown in FIG. 3B, the VCO gain K_(v) can have an inverse logarithmicrelationship with effective capacitance of the tunable capacitancecircuit. As effective capacitance increases, a decrease in VCO gainK_(v) has been observed in an inverse logarithmic relationship.

Additionally, in implementations with a plurality of VCOs, a VCO gainK_(v) vs. VCO frequency curve can include a plurality of sectionscorresponding to each VCO. Each of the plurality of sections can have asimilar shape and represent a similar relationship between VCO gainK_(v) and VCO frequency. FIG. 3C illustrates an example of therelationship between VCO gain K_(v) and VCO frequency in a synthesizerhaving a plurality of VCOs. As shown in FIG. 3C, a portion of the K_(v)vs. VCO frequency curve corresponding to each VCO can illustrate asimilar relationship. However, a corresponding slope and offset (whichcan also be referred to as an “intercept”) for each individual VCO maydiffer. This can be due to differences in VCO architectures.

In order to improve performance and/or stabilize loop bandwidth, overallloop gain can advantageously be kept substantially constant. One way tokeep overall loop gain constant is to compensate for VCO gain variation.This can be accomplished, for example, by adjusting the current in thecharge pump (e.g., charge pump 106 of FIG. 2) of the phase-locked loopusing a charge pump controller (e.g., charge pump controller 120 of FIG.2).

FIG. 4 is a flowchart of an illustrative method 200 of compensating forVCO gain variations. Any combination of the features of the method 200may be embodied in a non-transitory computer readable medium and storedin non-volatile memory. When executed, the non-transitory computerreadable medium may cause some or all of the method 200 to be performed.It will be understood that any of the methods discussed herein mayinclude greater or fewer operations and the operations may be performedin any order, as appropriate.

The method 200 can adjust the VCO gain so as to stabilize the overallloop gain of the phase-locked loop as any factor that can impact VCOgain changes. One example of a factor that can impact VCO gain is VCOout frequency as shown in FIG. 3C. Although more detail will be providedwith reference to VCO output frequency for illustrative purposes, otherfactors can be used as indicators of VCO gain in accordance with themethods and systems described herein. For example, VCO gain can dependon temperature and overall loop gain of the phase-locked loop can beadjusted to account for changes in temperature, for example, asdetermined via a temperature sensor.

By performing the method 200, the overall loop gain of the phase-lockedloop can be adjusted in parts that have not undergone factorycalibration related to charge pump current for factors that can impactVCO gain, such as VCO output frequency ranges. In addition, the method200 does not require additional programming related to factorycalibration by a controller prior to activation. Moreover, incompensating for an impact on VCO gain due to VCO output frequency, whenthe method 200 is performed in a PLL having a plurality of VCOs, acontroller may not need to obtain additional information regarding whichVCO is selected in the case where the VCO frequency is in an overlappingfrequency range in which more than one VCO can generate the VCOfrequency.

A VCO gain adjustment model can be selected based on an indicator of VCOgain at block 202. The VCO gain indicator can be indicative of anyfactor that can impact VCO gain, including, among other things, VCOoutput frequency and/or temperature. Since the VCO gain can be dependenton a indicator of VCO frequency (e.g., as shown in FIG. 3B), a chargepump controller can adjust the charge pump current to compensate for thechange in VCO gain due to the change in the indicator of VCO frequency.In some instances, the indicator of VCO frequency can be an effectivecapacitance in a tunable capacitance circuit for controlling VCOfrequency.

A VCO gain correction curve can correct for the variation of VCO gainbased on the indicator of VCO output frequency or other indicators thatVCO gain may be changing. Thus, a value on the VCO gain correction curvecan be provided to a charge pump controller to cause the charge pump tocompensate for the impact of VCO frequency on the VCO gain. Although theVCO gain correction curve corresponding to a VCO may not be linear, theVCO gain correction curve may be divided into a plurality of piecewiselinear gain adjustment models. Each of these models may correspond to arange of frequency indicator values. Accordingly, the VCO gainadjustment model can be selected based on a comparison of the indicatorof VCO frequency to one or more thresholds, which can represent valuesthat divide the VCO gain correction curve into separate linear gainadjustment models. In some implementations with multiple VCOs, thethresholds may be selected such that they are the same for each separateVCO.

The VCO gain adjustment models can include gain adjustment modelparameters. VCO gain adjustment model parameters can be obtained atblock 204. The model parameters can be any parameters from which a gainadjustment model can be created. For instance, the model parameters caninclude a slope and an intercept for a linear gain adjustment model. Thegain model parameters can be stored in memory and obtained by a readfrom memory. In implementations with multiple VCOs, the gain modelparameters can be obtained for the VCO selected to generate the VCOoutput. For example, the gain model parameters corresponding to each VCOcan be accessed from memory, and the gain model parameters for theselected VCO can be obtained using logic to select the gain modelparameters for the selected VCO.

Using the gain adjustment model parameters, a charge pump currentcontrol value can be computed at block 206. For example, using the VCOfrequency indicator, the charge pump current control value may be basedon the slope times the frequency indicator plus the offset for a lineargain adjustment model. The charge pump current control value can then beprovided to a charge pump that controls the overall loop gain of thephase-locked loop.

The overall loop gain of the phase-locked loop can be dynamicallyadjusted using the charge pump current control value at block 208. Thecharge pump can compensate for VCO gain variations without substantiallymodifying the VCO frequency. In this way, the overall loop gain of thephase-locked loop can be stabilized. As a result, the PLL can operatewith better performance and/or with stabilized loop bandwidth.

FIG. 5 is a block diagram of a charge pump controller 120 a, which isone example of the charge pump controller 120 of FIG. 2. The charge pumpcontroller 120 a can be included in a processor, such as a synthesizer.In some instances, the processor can include a PLL that includes thechange pump controlled by the charge pump controller 120 a. The chargepump controller 120 a can compensate for VCO gain variations, forexample, according to any combination of features of the method 200. Thecharge pump controller 120 can include a memory 222, a model selectblock 224, a VCO select block 226, and a charge pump current controlcalculator 228. The charge pump controller 120 can control VCO gainbased on any indictor of VCO gain, for example, an indicator of the VCOoutput frequency. In implementations with a plurality of VCOs, thecharge pump controller 120 a can also control the overall loop gain ofthe phase-locked loop based on the selected VCO.

The memory 222 can include RAM memory, flash memory, ROM memory, EPROMmemory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM,or any other form of storage medium known in the art. The memory 222 canstore threshold values and gain adjustment model parameters. In someinstances, the memory can include one or more lookup tables. In thisway, the thresholds and gain adjustment model parameters can be storedlocally in the charge pump controller 120 a so that these values do notneed to be derived and/or retrieved from a remote memory each time thesevalues are used.

The model select 224 can select a portion of a VCO gain correction curvebased on VCO frequency. The model select 224 can obtain one or morethreshold values from the memory 224 and an indicator of VCO gain, suchas VCO output frequency, from the VCO. Then the model select 224 cancompare the indicator of VCO gain to the one or more threshold values.From the comparison(s), a VCO gain adjustment model representing aportion of the VCO gain correction curve can be selected. The selectedVCO gain adjustment model can correspond, for example, to the VCO outputfrequency. The model select 224 can provide the charge pump currentcontrol calculator 228 with a model select indicator that indicateswhich VCO gain adjustment model to use to modify overall loop gain ofthe phase-locked loop based on the VCO gain indictor. For instance, thegain adjustment model can be selected based on a particular VCO outputfrequency.

The VCO select 226 can select one of a plurality of individual VCOs. Forinstance, a plurality of VCOs may be used to generate output signalsspanning a wide range of output frequencies, in which each individualVCO generates an output signal for a portion of the output frequencyrange. The VCO select 226 can obtain VCO gain adjustment modelparameters corresponding to a plurality of VCOs from the memory 224. Thegain adjustment parameters can include, for example, a slope and anoffset. The VCO select 226 can also obtain an indicator of the selectedVCO from the VCO. The indicator of the selected VCO can indicate whichof the plurality of VCOs is used to generate a VCO output at the VCOfrequency. Based on the indicator of the selected VCO, the VCO select226 can provide the charge pump current control calculator 228 with VCOgain adjustment parameters corresponding to the selected VCO.

The charge pump current control calculator 228 can compute a charge pumpcurrent control value based on the model select indicator from the modelselect 224 and the VCO gain adjustment parameters from the VCO select226. Using this data, the charge pump current control calculator 228 candynamically calculate the charge pump current control value for theselected VCO at a particular frequency. Using the charge pump currentcontrol value, the charge pump of the PLL (e.g., the charge pump 106 ofFIG. 3), can compensate for VCO gain variations so as to stabilize theoverall loop gain of the PLL.

FIG. 6 schematically illustrates a charge pump controller 120 b that candynamically adjust for VCO gain variations. The charge pump controller120 b is another example of the charge pump controller 120 of FIG. 2,which can be implemented in a processor, such as a synthesizer. In someinstances, the charge pump controller 120 b may also correspond to thecharge pump controller 120 a. The charge pump controller 120 b caninclude a lookup table component 232 and an arithmetic logic unit 234.

As illustrated, the lookup table component 232 includes three lookuptables: a threshold lookup table 242, a slope lookup table 244, and anoffset lookup table 246. Since the amount of data and/or the length ofdata entries may be different, each of the lookup tables 242, 244, and246 may be of different sizes. Alternatively, these three lookup tablescan also be implemented by any number of lookup tables. In someinstances, the lookup table component 232 can also store additioninformation for each VCO, including, for example, maximum VCO outputfrequency, minimum output frequency, maximum VCO gain, minimum VCO gain,and/or charge pump current control value range. Table 1 provides anexample of some of the values that can be stored in the lookup tablecomponent 232.

TABLE 1 Threshold TH1 TH2 TH3 TH4 TH5 TH6 TH7 18 35 51 67 83 98 113 VCO1 2 3 4 5 6 Slope x < TH1 0.875 0.625 1.125 1.625 1.125 1.75 TH1 <= x <TH2 0.9 0.7 1.2 1.7 1.3 2.05 TH2 <= x < TH3 0.95 0.8 1.3 1.8 1.5 2.375TH3 <= x < TH4 1.1 0.925 1.45 1.925 1.75 2.75 TH4 <= x < TH5 1.25 1.11.6 2.1 2.1 3.15 TH5 <= x < TH6 1.5 1.325 1.75 2.3 2.7 3.5 TH6 <= x <TH7 1.9 1.5 2.05 2.8 3.35 4.1 TH7 <= x 2.5 1.85 2.3 3.3 4.0 4.8 Offset x< TH1 1.25 1.25 1 1.75 1.5 2.25 TH1 <= x < TH2 1.51 1.44 1.34 2.24 1.842.78 TH2 <= x < TH3 1.78 1.65 1.70 2.75 2.23 3.39 TH3 <= x < TH4 2.021.85 2.02 3.20 2.60 3.98 TH4 <= x < TH5 2.24 2.03 2.31 3.58 2.95 4.53TH5 <= x < TH6 2.43 2.20 2.55 3.90 3.27 5.01 TH6 <= x < TH7 2.58 2.332.73 4.13 3.54 5.36 TH7 <= x 2.73 2.45 2.89 4.35 3.81 5.68

The values stored in the lookup table component 232 can provide all ofthe data to calculate a charge pump current control value based on anindicator of VCO gain (e.g., an indicator of VCO frequency) and anindicator of the selected VCO. Some or all of the values stored in thelookup table component 232 can correspond to, for example, a piecewiselinear representation of the VCO gain correction curves illustrated inFIG. 7. The VCO gain correction curves C1, C2, and C3 of FIG. 7 cancorrespond to charge pump current control values that can be used tokeep the overall loop gain of the phase-locked loop substantiallyconstant for different capacitance values in the tunable capacitancecircuit used to generate a VCO output signal. While three VCO gaincorrection curves are shown in FIG. 7, one VCO gain correction curve canbe determined for each VCO in a PLL. More detail regarding an example ofobtaining the values in the lookup table component 232 will be providedwith reference to FIG. 8.

The threshold values TH1-TH7 of FIG. 7 can be determined such that aportion of each VCO gain correction curve C1-C3 can be represented by alinear function. Accordingly, for portions of a VCO gain correctioncurve with a steeper slope, the thresholds may be closer together. Forexample, there is less difference between thresholds TH7 and TH6 thanbetween thresholds TH1 and TH2. In addition, there may be one lessthreshold than the number of linear partitions of the VCO gaincorrection curve, since n thresholds can divide a curve into n+1partitions. For instance, 7 threshold values can be used to divide a VCOgain correction curve into 8 linear partitions. The same thresholdvalues TH1-TH7 may be used for each VCO gain correction curve. Thethresholds can be indicative of VCO frequency. For instance, in theexample implementations of FIGS. 5-6, the thresholds can correspond to acapacitance value in a tunable capacitance circuit used to generate aVCO output. Each of the threshold values may be stored in the thresholdlookup table 242 of FIG. 6, and Table 1 provides example thresholdvalues. The size of the threshold lookup table 242 may be based on thenumber of threshold values stored times the number of bits used to storeeach threshold value. Thus, for more precise threshold valuesrepresented by more bits, the threshold lookup table 242 can be larger.

Each partition of a VCO gain correction curves C1-C3 can be representedby a linear VCO adjustment model. Since these models are linear, theycan be represented by a slope and an intercept. A charge pump gainGN1-GN3 can represent the difference between a value computed by a VCOadjustment model and the corresponding intercept or offset. The slopecan approximate the slope of the VCO gain correction curve for aparticular partition. The slope for each VCO can be stored in the slopelookup table 244. The size of the slope lookup table 244 may based onthe number of VCOs and the number of bits used to represent the value ofthe slope of each VCO. The intercept or offset can represent the pointat which the VCO gain correction curve intersects the y-axis. The offsetfor each VCO can be stored in the offset lookup table 246. The size ofthe offset lookup table 246 may based on the number of VCOs and thenumber of bits used to represent the value of the slope of each VCO. InTable 1, example slope and offset values are provided corresponding to aVCO gain adjustment model for each of 6 VCOs. In another implementation,one offset for each VCO can be stored and the offsets corresponding toeach VCO gain model can be derived from the stored offset.

The arithmetic logic unit 234 can read values from the lookup tablecomponent 232. The particular VCO gain adjustment model used tocalculate a charge pump current control value can be determined bycomparing a capacitance value of the tunable capacitance circuit thatcontrols VCO output frequency to the threshold values in the thresholdlookup table 242, for example, using one or more comparators 252. Thecapacitance value can be compared to any combination of the thresholdvalues from the lookup table 242. From the comparison(s), a model selectindicator can be generated. The slope and offset corresponding to eachportion of each VCO gain correction curve can be read from the slopelookup table 244 and the offset lookup table 246, respectively. Thevalues corresponding to the selected VCO can be selected, for example,using multiplexer(s) 254, based on an indicator from the VCO of whichVCO is selected to generate the VCO output.

The model select indicator can be used to select the slope and offsetcorresponding to the selected VCO gain adjustment model can correspondsto VCO output frequency. A charge pump current correction value CHARGEPUMP CONTROL can be computed by multiplying a capacitance segmentselection CAP_SEL by the selected slope SLP_VCO, for example, usingmultiplier 256. Then a selected offset OFS_VCO can be added, forexample, using adder 257. The capacitance segment selection CAP_SEL canbe obtained by comparing the current capacitance control with one ormore of the threshold values. In some implementations, the capacitancesegment selection CAP_SEL times the selected slope SLP_VCO can bedivided by a predetermined multiple (e.g., 8) for scaling purposesand/or ease of computation. This could be implemented either before orafter adding the selected offset. The division/scaling can beimplemented with a divider 258. The divider 258 can shift a value by 3bits, resulting in a division by 8. In such an implementation, thecharge pump current control value can be represented by the followingequation:

${CP\_ CTRL} = {\frac{{SLP\_ VCO} \times {CAP\_ SEL}}{8} + {{OFS\_ VCO}.}}$

In some instances, a bypass function may pass a predetermined chargepump current control value instead of the charge pump current controlvalue computed by the arithmetic logic unit 234. One way to implementthe bypassing functionality to is to use multiplexer 262 to select thecharge pump current control value calculated with the predeterminedcharge pump current control value using a bypass signal.

The VCO gain adjustment model parameters used for calculating a chargepump current control value may be derived using a number of differentmethods. The VCO gain adjustment model parameters may be obtained by aone time calibration, for example, during a factory calibration.Alternatively, the VCO gain model adjustment parameters may beauto-calibrated to account for additional variations.

FIG. 8 is a flowchart of an illustrative method 300 of calibrating VCOgain adjustment model parameters, according to an embodiment. The method300 can begin when a calibration event is detected at block 302. Thecalibration event is any event that can indicate that calibration cantake place. For example, the calibration event can be powering-up asystem that includes a VCO and a charge pump control. As anotherexample, a calibration event can be when a part operates above apredetermined temperature for a predefined period of time. Thecalibration event can trigger a calibration finite state machine.

At block 304, a frequency range and maximum VCO gain can be determinedfor each VCO. For example, the calibration finite state machine can tunea tunable capacitance circuit used to generate VCO frequency over therange of tunable capacitances and measure the output frequency range andan indicator of VCO gain. The VCO frequency can be proportional to aneffective capacitance in a tunable capacitance circuit used to generatea VCO output times a frequency of a reference clock provided to thephase-locked loop. The charge pump control current value range for eachVCO can be proportional to the maximum VCO frequency divided by theminimum VCO frequency cubed. This process can be repeated for eachindividual VCO in systems that include more than one VCO. With VCO gainmeasurements over a variety of frequencies, a VCO gain versus frequencycurve can be obtained for each VCO.

Once the VCO gain curve(s) have been obtained, the curve(s) can bedivided into a plurality of sections that can be represented bypiecewise linear models. One or more threshold values can be computed atblock 306 to determine where to divide the curve(s) into linear models.This can include, for example, determining points on the curve(s) thatcan be used to divide the curve(s) into roughly linear sections. Onenon-limiting example way, among others, to calculate threshold values isbased on determining a parasitic capacitance PAR_CAP and a charge pumpstep size CP_(STEP). The following equations can be used for the examplethreshold value calculation:

${PAR\_ CAP} = \frac{2^{CAP\_ BITS} - 1}{\left( {\max\left( {CP}_{RANGE} \right)} \right)^{\frac{2}{3}} - 1}$${CP}_{STEP} = \frac{\left( {2^{CAP\_ BITS} - 1 + {PAR\_ CAP}} \right)^{\frac{3}{2}} - ({PAR\_ CAP})^{\frac{3}{2}}}{{NUM\_ TH} + 1}$$\underset{\_}{\underset{\_}{{{TH}\lbrack j\rbrack} = {\left( {{{CP}_{STEP} \cdot j} + ({PAR\_ CAP})^{\frac{3}{2}}} \right)^{\frac{2}{3}} - {PAR\_ CAP}}}}$

In these equations, PAR_CAP can represent a parasitic capacitance of theVCO with the largest charge pump range, CAP_BITS can represent a numbercapacitance used for VCO tuning, Max(CP_(RANGE)) can represent a largestof all computed charge pump ranges, NUM_TH can represent a number ofthresholds used to partition the VCO frequency range into segments,CP_(STEP) can represent an incremental charge pump control step for eachsegment, and j can represent the j-th threshold value.

Gain adjustment model parameters can be computed at block 308. This caninclude, for example, deriving a slope and an intercept for each VCOgain adjustment. The slope and intercept of a curve can be derived usingany of the methods well known in the art. For illustrative purposes, anon-limiting example of an equation for computing the slope SLP and theintercept OFS is provided. The following example equations can be usedto derive the slope SLP and the intercept OFS:

$\underset{\_}{\underset{\_}{{{SLP}\lbrack i\rbrack} = {{{{CP}_{RANGE}\lbrack i\rbrack} \cdot {{OFS}\lbrack i\rbrack}} - {{OFS}\lbrack i\rbrack}}}}$$\underset{\_}{\underset{\_}{{{OFS}\lbrack i\rbrack} = \frac{{KV}_{MIN}\lbrack i\rbrack}{{KV}_{MIN}\left\lbrack \max \right\rbrack}}}$

In these equations, SLP[i] can represent a slope of the i-th VCO gainadjustment model, CP_(RANGE)[i] can represent the charge pump rangecovered between minimum and maximum frequency of the i-th VCO, OFS[i]can represent an intercept or offset of the i-th VCO gain adjustmentmodel, KV_(MIN) can represent a minimum VCO gain, and KV_(MIN)[max] canrepresent a minimum VCO gain of the VCO with the largest charge pumprange.

At block 310, the threshold values and gain adjustment model parameterscan be stored to memory. In some instances, these values can be storedto one or more lookup tables, for example, any of the lookup tablesdescribed in reference to FIG. 6. The threshold values and gainadjustment model parameters can later be read from memory and used tocalculate a charge pump current control value, which can be used tocompensate for VCO gain variations.

Some of the embodiments described earlier have provided examples inconnection with mobile devices. However, the principles and advantagesof the embodiments can be implemented in any other systems or apparatusthat have a need for adjusting a gain of an electronic oscillator, suchas a VCO. For example, any electronic device that includes a PLL mayadvantageously be improved by adjusting overall loop gain ofphase-locked loop as described herein.

Such systems can in implemented in various electronic systems and/orelectronic devices. Examples of electronic systems can include, but arenot limited to, consumer electronic products, parts of consumerelectronic products, electronic test equipment, etc. Examples ofelectronic devices can include, but are not limited to, a mobile phone(e.g., a smart phone), a telephone, a television, a computer monitor, acomputer, a hand-held computer, a tablet computer, a personal digitalassistant (PDA), a microwave, a refrigerator, an automobile, a stereosystem, a DVD recorder and/or player, a CD recorder and/or player, aVCR, an MP3 player, a radio, a camcorder, a camera (e.g., a digitalcamera), a portable memory chip, a washer, a dryer, a copier, afacsimile machine, a scanner, a multi-function peripheral device, awrist watch, a clock, etc. Further the electronic devices and/orelectronic systems can include unfinished products.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The words “coupled” or connected”, asgenerally used herein, refer to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Additionally, the words “herein,” “above,” “below,” and wordsof similar import, when used in this application, shall refer to thisapplication as a whole and not to any particular portions of thisapplication. Where the context permits, words in the above DetailedDescription using the singular or plural number may also include theplural or singular number respectively. The word “or” in reference to alist of two or more items, that word covers all of the followinginterpretations of the word: any of the items in the list, all of theitems in the list, and any combination of the items in the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of certain embodiments is not intended tobe exhaustive or to limit the invention to the precise form disclosedabove. While specific embodiments of, and examples for, the inventionare described above for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. For example, while processesor blocks are presented in a given order, alternative embodiments mayperform routines having steps, or employ systems having blocks, in adifferent order, and some processes or blocks may be deleted, moved,added, subdivided, combined, and/or modified. Each of these processes orblocks may be implemented in a variety of different ways. Also, whileprocesses or blocks are at times shown as being performed in series,these processes or blocks may instead be performed in parallel, or maybe performed at different times.

The teachings provided herein can be applied to other systems, notnecessarily the systems described above. The elements and acts of thevarious embodiments described above can be combined to provide furtherembodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A method of compensating for variations in avoltage-controlled oscillator (VCO) gain, the method comprising:selecting a VCO gain adjustment model based on a VCO gain indicator andat least one threshold value stored in a memory; obtaining VCO gainadjustment model parameters from the memory; computing a charge pumpcontrol value using the VCO gain adjustment model parameters; anddynamically compensating for VCO gain variations using the charge pumpcontrol value.
 2. The method of claim 1 wherein the VCO gain indicatoris indicative of a VCO output frequency.
 3. The method of claim 1wherein the VCO gain indicator is indicative of a capacitance value in atunable capacitance circuit configured to control a frequency of a VCOoutput.
 4. A method of claim 3 compensating for variations in avoltage-controlled oscillator (VCO) gain, the method comprising:selecting a VCO gain adjustment model based on a VCO gain indicatorindicative of a capacitance value in a tunable capacitance circuitconfigured to control a frequency of a VCO output, said selecting thegain adjustment model including comparing the capacitance value to athreshold value obtaining VCO gain adjustment model parameters from amemory; computing a charge pump control value using the VCO gainadjustment model parameters; and dynamically compensating for VCO gainvariations using the charge pump control value.
 5. The method of claim 1wherein the gain adjustment parameters include a slope and an offset. 6.The method of claim 1 wherein obtaining VCO gain adjustment modelparameters is based on a VCO selected from a plurality of VCOs.
 7. Themethod of claim 1 further comprising computing the VCO gain modelparameters, and storing the VCO gain model parameters to the memory. 8.An apparatus comprising a charge pump controller configured to select aVCO gain model based on a comparison of a VCO gain indicator and atleast one threshold value stored in a memory; obtain VCO gain modelparameters, from the memory, corresponding to the selected VCO gainmodel; and compute a charge pump control value using the VCO gain modelparameters.
 9. The apparatus of claim 8 wherein the VCO gain indicatoris indicative of VCO output frequency.
 10. The apparatus of claim 8wherein the VCO gain indicator is indicative of a capacitance value in acircuit configured to control a VCO output frequency, and the thresholdvalues stored in the memory represent threshold capacitance values. 11.The apparatus of claim 8 wherein the VCO gain model parameterscorrespond to a plurality of VCOs, and the charge pump controller isfurther configured to obtain VCO gain model parameters corresponding toone VCO selected from the plurality of VCOs.
 12. The apparatus of claim8 wherein the VCO gain model parameters include at least a slope and anoffset.
 13. The apparatus of claim 8 wherein the charge pump controlleris further configured to dynamically cause a gain of a VCO to beadjusted based on the charge pump control value.
 14. The apparatus ofclaim 8 wherein the VCO gain model represents a portion of a VCOcorrection curve, the VCO correction curve representing the VCO outputfrequency indicator versus the charge pump control value.
 15. Theapparatus of claim 8 further comprising a phase-locked loop, thephase-locked loop including a VCO and a charge pump, the charge pumpconfigured to receive the charge pump current control value from thecharge pump controller, and the charge pump further configured to adjusta gain of the VCO based on the charge pump current control value. 16.The apparatus of claim 8 wherein the charge pump controller is furtherconfigured to compute the VCO gain model parameters and the at least onethreshold value, and to store the VCO gain model parameters and the atleast one threshold value to the memory.
 17. The apparatus of claim 16wherein the charge pump controller is configured to compute the VCO gainmodel parameters in response to detecting a calibration event.
 18. Theapparatus of claim 8 further comprising the memory to store VCO gainmodel parameters and threshold values.
 19. The apparatus of claim 18wherein the memory includes at least one look-up table to store at leastone of the threshold values and the VCO gain model parameters.
 20. Anapparatus comprising: means for selecting a VCO gain model based on acomparison of a VCO gain indicator and at least one threshold valuestored in a memory; means for obtaining VCO gain model parameters fromthe memory corresponding to the selected VCO gain model; and means forcomputing a charge pump current control value using the VCO gain modelparameters.
 21. The apparatus of claim 20 configured as a base station.22. An apparatus comprising a charge pump controller, the charge pumpcurrent controller including: a memory configured to store VCO gainmodel parameters and threshold values; and an arithmetic logic unitconfigured to select a VCO gain model based on a comparison of a VCOgain indicator and at least one threshold value stored in the memory;obtain VCO gain model parameters, from the memory, corresponding to theselected VCO gain model; and compute a charge pump control value usingthe VCO gain model parameters.
 23. The apparatus of claim 22 wherein theVCO gain indicator is indicative of a capacitance value in a circuitconfigured to control a VCO output frequency, and the threshold valuesstored in the memory represent threshold capacitance values.
 24. Theapparatus of claim 22 wherein the arithmetic logic unit is furtherconfigured to obtain VCO gain model parameters corresponding to one VCOselected from a plurality of VCOs based on the comparison.
 25. Theapparatus of claim 22 wherein the VCO gain model parameters stored inthe memory include at least a slope and an offset.